Rhythmic chew cycles with distinct fast and slow phases are ancestral to gnathostomes.

Intra-oral food processing, including chewing, is important for safe swallowing and efficient nutrient assimilation across tetrapods. Gape cycles in tetrapod chewing consist of four phases (fast open and -close, and slow open and -close), with processing mainly occurring during slow close. Basal aquatic-feeding vertebrates also process food intraorally, but whether their chew cycles are partitioned into distinct phases, and how rhythmic their chewing is, remains unknown.

Do salamanders chew? An X-ray reconstruction of moving morphology analysis of ambystomatid intraoral feeding behaviours.

Chewing is widespread across vertebrates, including mammals, lepidosaurs, and ray-finned and cartilaginous fishes, yet common wisdom about one group-amphibians-is that they swallow food whole, without processing. Earlier salamander studies lacked analyses of internal kinematics of the tongue, analyses of muscle function, and sampled few individuals, which may have caused erroneous conclusions. Specifically, without tongue and food kinematics, intraoral behaviours are difficult to disambiguate.